Blood Vessels Flashcards
Describe continuous endothelium?
Endothelial cells which form a continuous sheet around lumen of vessels. The
only gaps are between adjacent endothelial cells. Found in muscle, skin, lung,
connective tissue
Describe fenestrated endothelium
Endothelial cells contain perforations of 50 - 60 nm. More permeable
than continuous endothelial cells. Found in kidney and villi of intestine
Describe discontinuous endothelium
endothelial cells have gaps up to 100 nm wide. Found in spleen and
liver.
What seperates the lumenal surface of endothelial cells from the lumen of blood vessels?
Glycocalyx, anegatively-charged complex of proteoglycans and glycosaminoglycans. It extends from 20 to 3000 nm off the luminal surface of endothelial cells. Appears to form a mesh with 20 nm spacing that may function as molecular sieve. Its negative charge impedes passage of negatively-charged (acidic) proteins.
What proteins anchor endothelial cells in blood vessels to the basement membrane?
Integrins
Name 3 compounds that induce gap junctions between adjacent endothelial cells
thrombin (as part of coagulation cascade), bradykinin (a dilatory factor), and histamine (as part of the inflammatory response)
How are gaps introduced between adjacent endothelial cells?
2 ways: disruption of proteins making up gap junction (occludins, claudins, and cadherins) or contraction of endothelial cells (by thrombin, very similar to muscle contraction)
What are selectins?
Proteins on the surfaces of leukocytes and endothelial cells. They generate adhesive forces between the two, and are expressed on endothelial cells in response to inflammatory factors
What are ICAM and VCAM?
Proteins expressed on endothelial cells in response to chemokines and chemoattractants. They tightly bind integrins on leukocytes as part of the arrest interaction
How do leukocytes exit blood vessels?
They activate the contraction of myosin filaments which pulls apart junctional complexes between endothelial cells. Leukoctyes then slide between endothelial cells, binding to different endothelial
junctional proteins
How does VEGF (Vascular endothelial growth factor) trigger angiogenesis?
VEGF causes endothelial cells to loosen connections with neighboring cells,
dissolve surrounding basement membrane and reverse polarity. Activated endothelial cells extend filopodia along VEGF gradients and also follow other guidance factors. Upon reaching a target vessel, migrating endothelial cells reestablish contacts and
form the lumen of the new vessel.
What are the three layers of blood vessels?
The tunica intima, media, and adventitia
Describe the tunica intima
The tunica intima comprises the endothelium, the adjacent basement membrane, the subendothelial connective tissue, and the internal elastic lamina; in smaller vessels, pericytes appear between layers of the split basement membrane of the endothelium
Describe the tunica media
The tunica media is composed of smooth muscle cells, elastic lamellae including the external elastic lamina and collagen fibers.
Describe the tunica adventitia
The tunica adventitia contains connective tissue, a few cells, macrophages, mast cells, fibroblasts, and the nerves and vessels that supply the vascular wall.
What is characteristic of elastic arteries?
Numerous concentric elastic lamellae of the tunica media interspersed with bundles of 2
smooth muscle cells. Elastic fibers in the media allow for the maintenance of blood pressure through the expansion and contraction of the vessel walls. Contains a vasa vasorum in their adventitia and outer part of the media
What is a vasa vasorum?
a network of small vessels that supplies the cells of larger vessels
Describe the tunica of the muscular arteries
The media of muscular arteries is composed of many concentric layers of smooth muscle cells arranged in a low angle helix, interspersed with less frequent and sometimes discontinuous elastic lamellae. The internal elastica marks the conventional boundary between intima and media. The external elastica separates the media from the adventitia. The media and adventitia of muscular arteries are approximately equal in
thickness.
What is the difference between arterioles and muscular arteries?
Arterioles contain no external elastic lamina, and the adventitia consists of a thin layer of collagen and isolated elastic fibers, whereas muscular arteries have adventitia as large as their media
What are sinusoids?
Capillaries with a discontinuous endothelium
What are pericytes?
contractile cells with long, branching processes that are
involved in the control of blood as it flows through the microvasculature, esp venules
What is diapedesis and where does it occur?
It is the exit of leukocytes from vasculature, and it occurs in venules, at labile junctions
What is special about vessels in the brain?
These arteries are rather thin-walled for their caliber, with a well-developed internal elastica and virtually no elastic fibers in the rest of the vascular wall. The veins have a thin wall devoid of smooth muscle cells.
What is special about pulmonary vessels?
These arteries have thin walls as a result of a significant reduction in both muscular and elastic elements, while the veins have a well-developed media of smooth muscle cells.
What is special about the umbilical vessels?
These arteries have two layers of smooth muscle cells without a prominent internal elastica or adventitia. The vein has a thick muscular wall with two to three muscle layers
